Fleming, as he says in his foreword, writes for “the educated general reader rather than the specialist.” A retired Princeton professor of medieval studies, he has spent the past several years reading about “alchemy, epistolary culture, Renaissance Egyptology, Jansenism, Pietism, the spread of Freemasonry in France, and the rise and decline of the literary salon.” The centerpiece of his book is an account of the mysterious Count Cagliostro, an alchemist, an adept at Egyptian magic, and, possibly — or possibly not — a consummate charlatan and con artist.

As a young scholar, Fleming was a student of D.W. Robertson Jr., renowned for the theological learning he brought to bear when interpreting medieval literature. (For examples of his method, see Robertson’s modest-sounding but truly magisterial “A Preface to Chaucer.”) So it’s no surprise that Fleming is at his best when he draws on his knowledge of Christian doctrine and belief. For instance, in his opening pages on Valentine Greatrakes, who effected seemingly miraculous cures by the laying on of hands, Fleming notes that “the Stroker” was said to smell like violets. He explains the implicit significance of this fragrant sweetness:

“For us, the phrase ‘odor of sanctity’ has only a metaphoric meaning, if it has any meaning at all. But the odor of sanctity was a real odor, sweet and floral, and in the old hagiographic texts, whether emanating from the living or the dead, was among the more common physical manifestations of divine spiritual approval.”

Throughout, Fleming consistently views the occult — i.e., the “hidden” — in spiritual terms. One early chapter, for instance, discusses “enthusiasm,” the emotional, impulsive side of religion that we associate with snake handlers and Holy Rollers. In “The Convulsionists” chapter, he interlaces accounts of miracles attributed to a saintly Francois de Paris with a precis of the antagonisms between the worldly Jesuits and the more austerely devout Jansenists. Speaking of a Bishop Massillon’s alarming sermon “On the Smallness of the Number of Those to Be Saved,” he writes:

“Massillon was no Jansenist, but it would be hard to distinguish his view of a Heaven with a population density roughly that of the Gobi Desert from the views of Augustine at his gloomiest.”

That’s neatly phrased, but sometimes Fleming comes across as offhand and flippant. When discussing magic, cabala, astrology and other recondite “sciences,” he tends to paraphrase and seldom conveys a sense of actual historical practice. Still, in a chapter on alchemy, he forcefully underscores that “the project of purification, amelioration, and transformation externally manifested at the forge betokened an inner transformation of the alchemist’s spirit.” In effect, the turning of base metal into gold (the technical term is spagyria) or the search for an elixir of life is secondary to true alchemy; what matters is self-exploration and self-transcendence. Just so, the Freemasons and Rosicrucians — whatever the actual origins of these secret societies — were initially churchlike sodalities devoted to the spiritual advancement of their members.

As Fleming reiterates about this period, “The mainstream of European thought was not materialist but sacramental. In the sacramental view, the material and visible world paralleled another that was immaterial and invisible.” Science, magic, religion — they are all attempts to understand what is hidden from us, and sometimes the three blur together. Isaac Newton, as is well known, left hundreds of pages of notes on alchemy and astrology. Benjamin Franklin was a member of an elite Freemason Lodge called “The Nine Sisters.”

If Fleming’s book, despite much interesting material, feels slightly rambling and inconclusive, Monod’s impresses by its scholarly detail. This is a serious yet lively work, chockablock with facts, anecdotes and original research. Its focus, however, is restricted to Britain and, as such, is both an extension of, and correction to, Keith Thomas’s classic “Religion and the Decline of Magic.” Monod doesn’t focus on folk practices or beliefs, however; instead, he studies written texts and how they were used.

Moreover, he early on makes clear a point similar to Fleming’s controlling theme: “The basic premise of occult knowledge is that a search for hidden causes in nature may lead towards something higher than nature: absolute wisdom, supernatural power or the divine.” Naturally such an ambition can readily verge on the heterodox, not to say the diabolical, given its echo of the serpent’s insidious promise, “You shall be as gods.”

If you were a would-be alchemist in the late 17th century, which books would you want in your library? Monod lists the top three: (1) “The Divine Pymander” of the legendary Hermes Trismegistus (this is a translation of the first 14 books of the “Corpus Hermeticum”); (2) Henry Cornelius Agrippa’s “Three Books of Occult Philosophy”; and (3) the “Ars Notoria,” often called the “Little Key of Solomon.” (Solomon has traditionally been viewed as a great magician.) This last, we are told, includes “a certain Magnetick Experiment” that would permit anyone to convey thoughts telegraphically to another person “by the virtue of the Loadstone.”

Loosely chronological and biographical in organization, “Solomon’s Secret Arts” opens with an account of a “respectable magus,” Elias Ashmole (whose cabinet of curiosities became the basis for Oxford’s Ashmolean Museum). To this well-off adept, alchemy presented “a Way to Bliss,” a road, in Monod’s phrase, “to personal fulfillment rather than to universal enlightenment.” Ashmole was convinced that the philosopher’s stone would permit communication with angels.

Thomas Vaughan — twin brother of the metaphysical poet Henry Vaughan — described himself as a “theomagus.” While Vaughan contributed a preface to a key Rosicrucian text, he denied any membership in the brotherhood, “a disclaimer,” as Monod wryly notes, “that was required of all true Brothers.” One of the first people to use the word “theosophy” in English, Vaughan was fascinated by the esoteric system for interpreting Scripture called Christian cabala, asserting that the Patriarch Jacob’s dream of a ladder to heaven revealed that “any man, with the help of spirits, might ascend to the divine.” Monod adds that Vaughan identified this mystical process with something called, eerily, “ ‘the Death of the Kiss, of which I must not speake one Syllable.’ ”

In its many subsequent pages “Solomon’s Secret Arts” examines Newton’s alchemical beliefs, Masonic symbols, William Blake’s visionary poetry, Gothic novels and much else. So take your choice: Fleming’s book is easy-going and essayistic; Monod’s is fact-filled and erudite. Happy synchronicity.

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